Project Summary Due to the high variability of neurological disease penetrance, it often remains difficult to predict an individual's health outcomes from genotype alone. Addressing this challenge, however, requires first understanding how brains vary in the absence of disease. The neural underpinnings of individual behavioral differences are largely unknown. This proposal seeks to use the fruit fly olfactory system as a model to investigate the neural sources of wild type behavioral individuality. Custom high-throughput behavioral instruments, two-photon imaging, and expansion microscopy of immunolabelled tissue will be used to characterize functional (Aim 1) and nanoscale structural (Aim 2) variation in the olfactory nervous system and how idiosyncrasies at these levels relate to individual odor preference behavior (Aims 1 and 2). Sufficiency of identified loci of individuality in modulating behavioral preferences will be tested using thermogenetic activators and inhibitors of defined neural subpopulations (Aim 3). Machine learning approaches will be used to analyze high-dimensional neural coding and structural data, automatically segment and label two-photon and confocal microscopy images, and train classifiers to predict behavior from idiosyncratic neural function and structure. Olfaction circuitry is highly analogous between flies and mammals, suggesting that principles of individuality discovered in flies may increase understanding of normal and pathological individuality in humans. These principles may explain why neurodevelopmental disorders such as autism and schizophrenia can play out differently among individuals with comparable risk factors. The proposed research will be carried out in the laboratory of Dr. Benjamin de Bivort in the department of Organismic and Evolutionary Biology at Harvard University. Dr. Aravinthan Samuel will co-mentor. The applicant's training plan includes learning experimental skills pertaining to Drosophila neurogenetics, advanced functional and structural neuroimaging techniques, and high-dimensional data analysis. The training plan also includes professional development training, such as responsible conduct of research, plans to present at international meetings, and extramural summer courses. The NIDCD Taste and Smell Program website states that the NIDCD supports studies of the central processing of chemosensory information including the underlying neural circuitry of central olfactory...brain regions. The proposed research will investigate variation in olfactory coding and behavioral preference and will therefore contribute to the NIDCD's future directions priority area #1, Understanding normal function, by increasing understanding of fundamental mechanisms of olfactory information processing in wild type animals. In addition, the proposed research will lay the groundwork toward a better understanding of neurological disorders that result in pathologically idiosyncratic neural function, such as autism, by explicitly characterizing how brains and behavior vary in the absence of disease. Thus, this proposal will contribute to NIH's overall mission of uncover[ing] new knowledge that will lead to better health for everyone.